(a) Field of the Invention
The present invention relates to a phase-cut pre-regulator and a power supply comprising the phase-cut pre-regulator.
(b) Description of the Related Art
In a power meter application, the power supply unit (PSU) should sustain a very high input voltage, with some customers stating 650 VAC in their specifications. Previous solutions have been to use a flyback converter to deliver the high input voltage to load directly. However, this has the following drawbacks.
One E-cap (electrolytic capacitor) cannot sustain the rectified voltage, and thus, two or more E-caps in series are needed. A voltage balance circuit must also be applied due to leakage current differences. However, limitations of the balance circuit will cause bad reliability, and multiple E-caps and balance circuits both cost money.
A switching device of a flyback should have more than 1500V breakdown voltage. Such devices always have higher switching and conducting losses and the price is high.
A secondary rectifier should also have a higher breakdown voltage. The forwarding voltage of an HV (high voltage) diode is higher than an LV (low voltage) diode, so the efficiency of high a Vin flyback will be lower.